Mux and sysex

[klausnielsen]

Hi everyone,
I'm working on a midi controller that will send out sysex to an old 80's synth. Using an example Pieter posted on Arduino Forum I can very easily get a single 10K potentiometer (hooked up to +5v, A0, GND) to send sysex in realtime (see below).
But since I will be needing a LOT of pots, I'm thinking I need to use multiplexers similar to the example on CCPotentiometers given in section 4 of the 'Getting Started' documentation. I've searched high an low for examples on how to do this, but without luck. How would you go about muxing this sysex sketch?
Hope someone has some ideas
Cheers

// Include the library
#include <Control_Surface.h>

// Select the serial port to use.
auto &serial = Serial;

// Instantiate a Serial MIDI interface at the default MIDI baud rate.
SerialMIDI_Interface<decltype(serial)> midi {serial, MIDI_BAUD};

// Reads, filters and detects changes of an analog input
// Produces a 7-bit output [0-127]
FilteredAnalog<7> potentiometer { A0 }; 

// MIDI System Exclusive data to send - VCF Freq
uint8_t sysex_data[] {
  0xF0, 0x10, 0x06, 0x06, 0x15, 0x00, 0xF7,
};
// Reference to easily update the parameter value of the SysEx message
uint8_t &vcf_value = sysex_data[5];

void setup() {
  // Initialize MIDI interface and analog input
  midi.begin();
  potentiometer.setupADC();
}

void loop() {
  midi.update(); // Handle and discard MIDI input

  // Check whether the potentiometer value changed
  if (potentiometer.update()) {
    vcf_value = potentiometer.getValue(); // if it did, update the message
    SysExMessage msg { sysex_data, sizeof(sysex_data) };
    midi.send(msg); // and send it out over MIDI
  }
}

[tttapa]

You could create an array of FilteredAnalog, and use mux.pin(p) instead of A0. Then simply loop over all potentiometers and send the appropriate value using a for loop.

CD74HC4067 mux { ... };

FilteredAnalog<7> potentiometers[] {
  mux.pin(0), mux.pin(1), // ...
};

Some examples that could be useful:

• https://tttapa.github.io/Control-Surface-doc/Doxygen/d2/d96/3_8FilteredAnalogReadSerial_8ino-example.html
• https://tttapa.github.io/Control-Surface-doc/Doxygen/d4/d3b/Custom-MIDI-Output-Element_8ino-example.html

[klausnielsen]

Thanks, Pieter, for taking the time to answer all of these questions. I see your point about creating an array of FilteredAnalog with the mux pins, but I'm having a hard time figuring out how to assign a different sysex address to each mux pin (which was super easy and smooth with CCPotentiometer.)
I'm sure the answers is somewhere in the two examples you reference, but I cannot crack the nut. I would be super grateful if you could please show me how you would make for instance mux.pin(0) send out sysex_data[5] values for the sysex string {0xF0, 0x10, 0x06, 0x06, 0x15, 0x00, 0xF7} and mux.pin(1) send out sysex_data[5] values for {0xF0, 0x10, 0x06, 0x06, 0x16, 0x00, 0xF7}. (Index[4] of course being the sysex parameter ID.) I could hopefully pick up from there.

[tttapa]

If you want something similar to CCPotentiometer, you could try something like this (untested):

#include <Control_Surface.h>

uint8_t sysex_data[] {
  0xF0, 0x10, 0x06, 0x06, 0x15, 0x00, 0xF7,
};

class SysExPot : public MIDIOutputElement {
 public:
  SysExPot(pin_t pin, uint8_t param_id)
    : pot(pin), param_id(param_id) {}

  void begin() final override {
    pot.resetToCurrentValue();
  }

  void update() final override {
    if (pot.update())
      send(pot.getValue());
  }

  void send(uint8_t value) {
    sysex_data[4] = param_id;
    sysex_data[5] = value;
    Control_Surface.send(SysExMessage{sysex_data});
  }

 private:
  FilteredAnalog<7> pot;
  uint8_t param_id;
};

auto &serial = Serial;
SerialMIDI_Interface<decltype(serial)> midi {serial, MIDI_BAUD};

CD74HC4067 mux {A0, {3, 4, 5, 6}};

SysExPot pots[] {
  {mux.pin(0), 0x15},
  {mux.pin(1), 0x16},
};

void setup() {
  Control_Surface.begin();
}

void loop() {
  Control_Surface.loop();
}

See the Custom-MIDI-Output-Element example from my previous post for more information about the functions I defined in the SysExPot class.

[klausnielsen]

Fantastic! It works right out of the box :)
Thanks Pieter - I really appreciate your help.
I will be sure to test this in the coming weeks - pushing it as far I can. (Will be needing 64 pots or so + a number of push buttons.)
Already I see the next challenge: Some pots need to go from 0-127, while others will need to go from 0-63 or from -63 to +63(!) I will have some stuff to learn :)